North Korean leader Kim Jong-un has vowed to shut down the country's nuclear test site in May and open the process to experts and journalists from South Korea and the United States, Seoul's presidential office has said.

Key points:

Singapore is being considered as a location for the Trump-Kim summit

Mr Trump said he would continue to sanctions pressure on Pyongyang

He is also providing the Japanese Prime Minister with updates on the negotiations

Mr Kim made the comments during his summit with South Korean President Moon Jae-in on Friday (local time), where he also expressed optimism about his anticipated meeting with Donald Trump.

The North Korean leader said the US President would learn he is "not a person" to fire missiles toward the United States, Mr Moon's spokesman Yoon Young-chan said.

During the summit, the two Korean leaders promised to work toward the "complete denuclearisation" of the Korean Peninsula, but made no references to verification or timetables.

Seoul had also shuttled between Pyongyang and Washington to set up a potential meeting between Mr Kim and Mr Trump, which is expected next month or early June.

"Once we start talking, the United States will know that I am not a person to launch nuclear weapons at South Korea, the Pacific or the United States," Mr Yoon quoted Mr Kim as saying.

"If we maintain frequent meetings and build trust with the United States and receive promises for an end to the war and a non-aggression treaty, then why would be need to live in difficulty by keeping our nuclear weapons?"

Earlier, at a campaign rally in Michigan, Mr Trump announced his meeting with the North Korean leader would be held "over the next three or four weeks".

"It's going be a very important meeting, the denuclearisation of the Korean Peninsula," he said.

Mr Trump has also spoken with the leaders of South Korea and Japan ahead of his unprecedented meeting with Mr Kim.

Earlier, he tweeted about having "a long and very good talk" with South Korean President Moon Jae-in.

"Things are going very well, time and location of meeting with North Korea is being set," he said.

"Also spoke to Prime Minister Abe of Japan to inform him of the ongoing negotiations."

Mr Moon's office said during the phone call, Mr Trump agreed that the summit between Mr Kim and the US President should be held soon, with Mr Trump telling the South Korean leader the meeting would take place over the next three to four weeks.

Mr Trump and Mr Moon exchanged views on two to three possible locations for the meeting, according to the South Korean leader's office.

A senior US official said Singapore is being considered as a possible venue for the Trump-Kim summit.

North Korea suspends nuclear tests, will change time zone

Mr Kim reacted to scepticism that the North would only be closing down the northernmost test tunnel at the site in Punggye-ri, which some analysts say became too unstable to conduct further underground detonations following the country's sixth and most powerful nuclear test in September.

In his conversation with the South Korean President, Mr Kim denied that he would be merely clearing out damaged goods, saying that the site also has two new tunnels that are larger than previous testing facilities, Mr Yoon said.

Mr Yoon said the North Korean leader also revealed plans to re-adjust its current time zone to match the South's.

The Koreas used the same time zone for decades before the North in 2015 created its own "Pyongyang Time" by setting the clock 30 minutes behind South Korea and Japan.

North Korea explained the decision as an effort to remove a legacy of Japanese colonial rule.

Local time in South Korea and Japan is the same — nine hours ahead of Greenwich Mean Time (GMT).

It was set during Japan's rule over the Korean Peninsula from 1910 to 1945.

Mr Yoon said that the North's decision to return to the Seoul time zone was aimed at facilitating communication with South Korea and also the United States.

Turnbull praises Trump for bringing Korean leaders together

Meanwhile, Prime Minister Malcolm Turnbull has praised Mr Trump's negotiations on North Korea, saying he had helped bring the two Korean leaders together.

"I have given him that credit because Donald Trump has taken a very, very strong hard line on the denuclearisation issue and he has been able to bring in the support of the global community and, in particular, China," Mr Turnbull said.

"North Korea's economic relationship is overwhelmingly with China. And so China's preparedness to impose those sanctions has been the critical change that has put the economic pressure on North Korea."

Mr Turnbull said the pressure from China and the US had brought Mr Kim to the point of denuclearising the Korean peninsula.

"What we've now got to do is not relent on the economic pressure until that goal is achieved," he said.

North Korean media covers historic Kim, Moon visit

A day after the meeting between Mr Kim and Mr Moon produced dramatic images and a sweeping declaration of goodwill, South Korean media were replaying striking scenes of the two leaders and North Korea's main state newspaper published a multi-page spread with more than 60 photos from the visit.

On Saturday afternoon, North Korean state TV broadcast its first footage of the summit.

Most of the specific commitments outlined in the official declaration focused on inter-Korean relations and did not clear up the question of whether Pyongyang is willing to give up its arsenal of nuclear weapons and ballistic missiles.

In their coverage of the summit, North Korean state media made rare mentions of the denuclearisation discussion, but did not go into specifics, instead highlighting the broad themes of peace, prosperity, and Korean unity.

The declaration earned guarded but optimistic praise from world leaders, including Mr Trump, who said that only time would tell, but that he did not think Mr Kim was "playing".

"It's never gone this far. This enthusiasm for them wanting to make a deal ... We are going to hopefully make a deal."